Depth-controlled drill presses

ABSTRACT

A depth-controlled drill press having a supporting means including a head slidably mounted in the body of said supporting means and manually movable toward and from a work rest carried by the body, a quill rotatably mounted in said body and held from axial movement, a motor rotating said quill, a tool supporting spindle received within said quill guided for axial movement and restrained from rotation relative to the quill. The upper end of the spindle is held attached to said head by an electromagnet and pushed away from the work by a spring when the electromagnet is deenergized by circuitry actuated upon the tool engaging a metallic member in the work.

United States Patent [72] Inventor Ralph S. Thacker 4434 Los FelizBlvd., Los Angeles, Calif. 90027 May 12. 1969 July 27, 1971 [21 Appl.No. [22] Filed [45] Patented 54] DEPTH-CONTROLLED DRILL PRESSES 12Claims, 4 Drawing Figs.

Primary Examiner-Gil Weidenfeld At1arneylkel,C. Benson ABSTRACT: Adepth-controlled drill press having a supporting means including a headslidably mounted in the body of said supporting means and manuallymovable toward and from a work rest carried by the body, a quillrotatably mounted in said body and held from axial movement, a motorrotating said quill, a tool supporting spindle received within saidquill guided for axial movement and restrained from rotation relative tothe quill. The upper end of the spindle is held attached to said head byan electromagnet and pushed away from the work by a spring when theelectromagnet is deenergized by circuitry actuated upon the toolengaging a metallic member in the work.

PAIENIED .mLznsm sum 1 [IF 3 INVENTOR.

RALPH 5. THACK ER ATTORN EY FIG.3

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ATTORNEY DEPTH-CONTROLLED DRILL PRESSES FIELD OF THE INVENTION PRIOR ARTThe prior art known to applicant shows an electric motor for driving thetool and circuitry operated by the tool contacting the conductor andstopping the motor.

SUMMARY OF THE INVENTION Applicant greatly reduces the time cuttingcontinues after contact is made by raising the tool from the work whilethe tool is rotating instead of stopping the motor and the tool.

In the drawings illustrating an embodiment of the invention:

FIG. 1 is a plan view of the structure shown.

FIG. 2 is an elevational view of part of the structure shown in FIG. 1.

FIG. 3 is a fragmentary sectional view taken on line 3-3 of FIG. 1 anddrawn to a greater scale.

FIG. 4 is a wiring diagram of the invention.

The invention comprises supporting means A which includes a body B and ahead C slidably mounted therein. The body B is mounted for verticaladjustment on a standard 30 mounted on a base D. A work rest F andtemplate supporting means G also are mounted on the base D. Rotatablymounted in the body is quill means H and rotatable with said quill andslidable along the same is a spindle I. Feed means M moves the cuttertoward and from the work rest. Shifting means I includes electromagneticmeans which connect the spindle l to the head C and a spring whichshifts the spindle away from the work. Control means K controls theoperation of the shifting means J and power means L powers the spindle Ithrough the quill H.

BASE

The base D, best shown in FIGS. I and 2, has sidewalls II and end walls12 and I3. The rear ends ofthese sidewalls have upwardly projectingextensions I4 formed with forwardly inclined edges I5. Walls I6corresponding in configuration with the extension 14 are disposedinwardly of said extensions. The rear end wall I3 extends completelyacross the extensions 14 and walls I6 and is the full height of saidwalls and extensions and ties all of the parts together. Between thewalls 16 and the extensions I4 are tops 21 and inclined walls 22. Thisconstruction provides two compartments 23 within said walls andextensions and an open space 24 between the walls I6. Across the wallsI6 at the lower portion of the same is a shelf 25 which is integral withthese walls and the rear end wall I3.

Resting on the shelf 25 is a tubular standard 30 which has a cylindricalupright 31 with a flange 32 issuing outwardly therefrom at the lowermostportion thereof. This flange rests upon the shelf 25 and is held inposition thereon by means of capscrews 33 which extend through saidshelf 25 and are screwed into the flange 32.

BODY

The supporting means A comprises the body B best shown in FIGS. I and 3.This body is cast and has a rear section 40, a front section 130 and anintermediate section 50.

The rear section 40 of body B is substantially square in cross sectionand has a vertical bore 41 in the same receiving the upright 31 andguiding said body for vertical sliding movement in an up and downdirection. By means of this construction, the section 40 is formed withsidewalls 42, a front end wall 43 and a rear end wall 44. A cover 45closes the open upper end of the bore 41.

The intermediate section has a top wall 51, a bottom wall 52, a rear endwall 53, a front wall 54, and a sidewall to form a chamber 56 within thesame. This chamber 56 is closed by a cover 61 attached to the walls 51,52, 53 and 54 by means of screws 62. I I

Means for raising and lowering the body B consists of a pinion 63attached to a shaft 64 journaled in a bearing 65 issuing from thesidewall 55 of section 50. Upon the end of the shaft 64 projectingbeyond the bearing 65 is a handwheel 67 which is secured thereto and bywhich the pinion 63 may be rotated. This pinion meshes with a rack 66secured to the upright 31 of standard 30.

For holding the body B in position, clamping means 70 is provided whichis shown in FIG. 3 and which is constructed by forming the lower end ofthe rear section with a transverse slit 71 extending wall toward thecenter of said upright. A vertical slit 72, FIG. I, divides the portionof the lower part 73 formed by slit 7] into jaws 74. By means ofa screw75 passing through one of said jaws and screwed into the other, the jawsmay be drawn together to clamp the section 40 and thus the entire body Bto the upright 30 and thus to base D.

WORK REST The space 18 between the front end wall 12 and a cross wall 17intermediate the two end walls is open at the top. In this space islocated the work rest F. This work rest is supported on two parallellongitudinal guide rods 81 and 82, which are spaced from the sidewalls11 and are secured to the front end wall 12 and to the cross wall 17 ofbase D. Slidably mounted, for longitudinal movement along these rods, isa frame 83 which has lateral frame members 84 and 85 and longitudinalframe members 86 and 87. The space 88 between these frame members isopen. The frame members 86 and 87 are bored longitudinally to receivethe rods 81 and 82 which guide the frame for longitudinal movementrelative to base D. In the space 88 are two transversely spaced parallelrods 91 and 92 which are spaced from the frame members 84 and 85 andwhich are attached to the frame members 86 and 87. Slidably mounted onthese rods is a table 93 on which the work is mounted. A part ofspecimen 94 is shown which is held in position on said table by one ormore clips 95 having screws 96 passing through them and screwed intosaid table.

TEMPLATE SUPPORTING MEANS The template supporting means G consists of aframe 100 having longitudinal frame members 101 and I02, and transverseframe members I03 and 104. These frame members are rabbeted to form agroove I05 and which receives a standard template, a portion of one ofwhich has been shown in FIG. I as inserted in the groove I05 andindicated by the reference numeral 106. This template lies flush orslightly below the top of the frame 100 and which is held in place bycountersunk screws 107 which lie flush with or below the surface of theframe 100. The frame 100 is slidably mounted in a transverse slot 111,FIG. I and FIG. 2 in the wall 12 of bore D, and in which it can moveboth longitudinally and transversely of said base. The rear end II2 ofsaid frame is attached to the table 93 by screws I13 and moves with saidtable in either or both directions. A handle IN is attached to the outerend of frame 100 and by which both said frame and table can besimultaneously moved. I

Above the frame I00 is a guide and which guides for vertical slidingmovement a pin I16 which has a head II7 by means of which the same maybe manipulated. This pin has a reduced end 118 adapted to enter locatingholes 119 in the template 106 to place the work 94 in proper positionfor cutting.

HEAD

The head C consists ofa casting 120 which overlies the forward sectionof the body B and also a portion of the intermediate section 50 of saidbody. In the section 130 is formed a vertical bore 131 in which isreceived a guide 132 which has a cylindrical guideway 133. The bore 131is reduced in diameter at its lower end as indicated at 134 in FIG. 3 toform a shoulder 135 therebetween. The tubular guide 132 is received inthe bore 131 and rests on the shoulder 135. A tubular plunger 137 ispressed into a socket 138 in head 120 and held therein. The plunger 137is received in the bore 133 in the guide 132 in Section B and guides thehead C for movement toward and from the body B.

QUlLL Quill means H is best shown in FIG. 3 and comprises a quill 140which is received in a bore 141 in the forward section 130 of body B.This bore 141 has a considerably greater diameter than the diameter ofsaid quill so as to form a sizable annular space 142 therebetween. Thequill 140 is joumaled in two ball bearings 143 and 144 received in thebore 141. The outer race 146 of the bearing 143 butts up against ashoulder 147 in the body B while the inner race 151 butts up against ashoulder 152 on the quill 140. Bearing 144 is mounted in a similarmanner to bearing 143. The quill 140 has a bore 154 extending throughoutthe length thereof which is enlarged at its ends to receive two guides155 and 156. These guides have aligning bores 157 and 158.

SPlNDLE The spindle 1 is constructed of a solid rod which is received inthe bores 157 and 158 of the guides 155 and 156 for sliding movementtherein. The lower end of this spindle is tapered as indicated by thereference numeral 162 for the mounting of a drill chuck 163 thereon andin which any suitable cutter may be inserted. The spindle l is held fromrotation relative to the quill 140 by means of a diametrically extendingpin 164 which extends through and is slidable along two longitudinaldiametrically disposed slots 165 and 166 in the quill 140. By means ofthis construction the spindle I may travel longitudinally relative tothe quill 140 and rotates in unison with said quill.

Encircling the lower end of the quill 140 is a main compression coilspring 171 which is seated at its lower end in a spring seat 172 restingon the inner race of the bearing 144. The pin 164 is of greater lengththan the diameter of the quill 140 and the upper end of the spring 171is seated against the protruding ends of this pin-Above the pin 164 isbuffer compression coil spring 173 encircling quill 140 and which isseated at its lower end against the pin 164 and at its upper end againsta spring seat 174 which engages the inner race 151 of bearing 143. Asleeve 175 encircles the springs 171 and 173 as well as the pin 164 andholds these parts in operative positions. The spring 171 is stiffer thanthe spring 173 and urges the pin 164 against the portions of quill 140at the upper ends of the slots 165 and 166.

Sl-llFTlNG MEANS The shifting means J comprises electromagnetic means180. Mounted on the upper end of spindle l is an electromagnet 181 whichis freely rotatable thereon. A ball bearing 182 disposed on the end ofspindle l and seated in a socket 183 in electromagnet 181 supports thespindle l for rotation relative to said electromagnet. An annular collar184 carried by said electromagnet holds the bearing 182 in place insocket 183. The electromagnet 181 has a conical portion 185 at the lowerend of the same and which is inverted. Encircling the conical portion185 and spindle I is an electric coil 186 which has a core 187 securedto the casting 120 by means of screws 188. This core has a conicalsocket 189 adapted to receive the conical portion 185 of electromagnet181.

FEED MEANS spindle l and also to the plunger 137 and is slidable througha' hole 122 in the-top wall 51 of intermediate section 50 of body 13 andinto the chamber 56 therein. This rod has a rack 123 secured to it whichmeshes with a gear 124 in said chamber and which is secured to a shaft125. This shaft is rotatably mounted in a bearing 126 formed on anattachment 127 secured to the sidewall 55 of intermediate section 50 ofbody B by screws 128. The shaft extends outwardly through the cover 61over chamber 56 and has attached to it a handwheel 129 by which the gear124 may be rotated to raise or lower the spindle l and to feed thecutter carried thereby to the work.

POWER MEANS The power means L includes an electric motor 190 which hasattached to it two brackets 191 which are slidable in slots 192 on eachof the sidewalls 43 of the rear section 40 of body B. Screws 193 passingthrough a flange 194 connecting said brackets together are screwed intothe base 195 of motor 190 and hold the motor attached to the brackets.Capscrews 196 having washers 197 thereon pass through slot 198 inbrackets 191 and are screwed into the walls 43 of the rear section 40 ofbody B, thus guiding the motor 190 for movement toward the quill 140. iI

The armature to shaft 201 of the motor 190 has mounted on it a pulley202. Extending about this pulley and another pulley 203 on quill is abelt 204 which rotates the quill 140 and the spindle l. The casting120'has slots 205 in the lower portion of the same which receive theruns of the belt 204 when the head is lowered.

HOLDING MEANS The holding means N is shown in detail in FIG. 3. Sincethe conductors to be cleaned of outer insulation are fiat and generallythin, cutting must be closely controlled. To hold the work down tightagainst the table 93 the holding means N is used. This holding meanscomprises a foot 210 which is detachably secured to the end of a smallrod 211 by means of a screw 212. ln the bore 139 of plunger 137 isslidably mounted a slider 213 which is drilled at its lower end asindicated by the reference numeral 214 to receive the rod 211. The lowerend 215 of the slider 213 is conical and is split longitudinally. A nut216 similarly constructed is screwed on the end of said slider and whentightened holds the rod 211 in adjusted position in the drilled hole 214of said slider. The slider 213 is held from rotational movement relativeto the plunger 137 by means of a key 217 issuing from said slider andslidable along a keyway 288 formed in said plunger. The slider 213 isurged downwardly by means of a compression coil spring 221 disposed inthe bore 139 of plunger 137 and seated at its lower end against theupper end of the slider 213 and seated at its upper end against a springwasher 223 attached to the upper end of plunger 137.

CONTROL MEANS The control means K comprises circuits shown indiagrammatic form in FIG. 4. Power is derived from any 1 15 voltalternating-current source by line conductors 241 and 242. The motor isoperated by a motor circuit 240. Motor 190 may be a split-phasesingle-phase alternating-current motor having an armature 243, a runningwinding 244 and a starting winding 245. Conductor 241 is directlyconnected to one end of the'winding 245 and by a conductor 249 to thewinding 244. Connected to the line conductor 241 by a conductor 247 is apilot lamp 251 which is connected by a conductor 252 to a resistor 253.This resistor by a conductor 248 is connected to one terminal 254 of atwo-way switch 255. The movable arm 256 of this switch is connected tothe line conductor 242. Another pilot lamp 261 is connected by aconductor 262 to line conductor 241 and by a conductor 263 to a resistor264. This resistor is connected by a conductor 265 to the other terminal266 of switch 255. A second conductor 267 is connected to the terminal266 and directly to the running winding 244 and through centrifugalswitch 246 to the starting winding 245. Lamp 251 indicates when themotor is off and lamp 261 indicates when power has been applied to themotor.

The control means K further includes a direct-current low voltage powersupply 270. This power supply includes a double-pole double-throw switch271 having terminals 272, 273, 274 and 275 and arms 276 and 277. The arm277 is connected by a conductor 281 to the line conductor 241. The arm276 is connected by a conductor 282 to the line conductor 242. Terminal272 is connected by a conductor 283 to one end of the primary 284 of atransformer 2B5. Terminal 274 is connected by a conductor 286 with theother end ofthe primary 284 of transformer 285. Terminal 273 isconnected by a conductor 287 with a lamp 291. This lamp is in turnconnected by a conductor 292 to a resistor 293, which in turn isconnected by a conductor 294 to the terminal 275 of switch 271.Illumination of lamp 291 indicates that the transformer is notenergized. One end of the secondary 295 of the transformer 285 isconnected by a conductor 296 to one input terminal 334 of a rectifier297 and the other end of said secondary of transformer 285 is connectedby means of a conductor 298 to the other input tenninal 335 of therectifier 297.

The control means K further includes a normally closed relay 300 havinga coil 301 and two contacts 302 and 303. In addition, the control meansincludes a conductor 310 which has two terminals 311 and 312. Any typeof connector such as is now well known in the art may be used. Theterminals 311 and 312 may be prongs such as are used with electricalinstruments or clips for temporarily making contact with the metal ofthe work. If sharpened, the prongs readily puncture the insulation andmake contact with the metal of the work and may be held in positionmanually. If many spots are to be cleaned, clamps, screws, or clips maybe used in the customary manner to hold the terminal attached to thework with the terminals 311 and 312 in contact with the metal of thework. Connected to the negative output terminal 337 of the rectifier 270is a conductor 304 which is connected to one end of the coil 301 ofrelay 300. The plus output terminal 336 of the rectifier 297 isconnected by a conductor 317 to the terminal 312 of conductor 310. Theother end of coil 301 is connected by a conductor 305 to a cutter 306mounted in the chuck 163. This conductor is grounded to the body B andBase D. The solenoid coil 186 is connected at one end by a conductor 314to the conductor 304 and thus to the negative output terminal 337 of therectifier 297; a conductor 315 connects the other end of the coil 186with the contact 303 of relay 300. The other contact 302 of said relayis connected by a conductor 316 with the other terminal 311 of saidconductor. A pilot light 321 is connected across conductors 304 and 315by conductors 322 and 323 and thus across the coil 186 ofelectromagnetic means 180. Another pilot light 324 is connected by meansof conductors 325 and 326 to conductors 304 and 305 and thus across coil301 of relay 300. Still another pilot light 331 is connected by means ofconductors 332 and 333 to conductors 296 and 298 and thus across theoutput of rectifier 297.

In cutting insulation from flat conductors, it becomes desirable toremove a slight amount of the metal at the surface thereof to facilitatesoldering thereon. In order to accomplish this result the operation ofthe shifting means is delayed a short period of time. This isaccomplished by time-delay means 340, utilizing capacitors and switches.This means utilizes a rotary switch 341 having six contacts 342, 343,344, 345, 346 and 347 and a switch arm 348 rotatable to contact any ofsaid contacts. These contacts are connected by conductors 352, 353, 354,355, 356 and 357 to capacitors 362, 363, 364, 365, 366 and 376 which, inturn, are connected by conductors 372, 373, 374, 375, 376, 377 to acommon conductor 351. Conductor 351 is connected to conductor 315. Aconductor 371 connects the switch arm 348 to conductor 314. Thecapacitors 342, 343, 344, 345, 346 and 347 are of different values sothat different timing can be procured as desired. Flexible conduits 351and 352 conduct the conductors to the motor 190 and coil 186.

The operation of the invention is as follows: With no power applied, thedrill 306 is inserted into the chuck 163 and the body B raised onstandard 30 by means of handwheel 67 until the drill is a considerabledistance above the work. The head C is then lowered to its lowermostposition by handwheel 129 and in which said head rests upon the uppersurface of body 13. The entire body B is next lowered on standard 30 byrotating handwheel 67 until the end of the drill is just above theinsulation on the work and said body locked in position by clampingmeans 70. So disposed, the drill can not enter the work. Head C is nowraised by means of handwheel 129 a distance greater than maximummovement of the electromagnet 181 relative to core 187 by means of thehandwheel 129. When switch 271 is in the opposite position from thatshown in FIG. 4, the pilot light 291 is lighted indicating that electricpower is available. When switch 255 is moved to the position shown inFIG. 4, light 261 is lighted and motor 190 energized. When in theopposite position, light 251 is lighted and the motor shut off. When thedrill press is in use, the motor 190 runs continuously. When switch 271is in the position shown in FIG. 4, the transformer 285 is energized anddirect current is available at a lower voltage than the line voltage andat the output terminals 336 and 337 of the rectifier 297. Pilot light331 is then lighted showing that direct current is available. Theconnector 310 is next applied to the work with the terminals 311 and 312making contact with the metal of the work, the insulation of which is tobe removed. With the power on a completed circuit may now be traced. Thecurrent flows from the plus terminal 336 of rectifier 297 throughconductor 317 the point 312 of connector 310, the conductor beingcleaned, point 311, metal of the work 316 contact 302 of relay 300,through the contact 303, conductor 315, coil 186 of electromagneticmeans and conductor 314 and 304 to the negative terminal 337 ofrectifier 270. The electromagnet 181 is now attracted to the core 187and the spindle I still rotating is drawn in a downward direction, itsmotion terminating when the electromagnet strikes the core 187. Cuttingmay now proceed by rotating the handwheel 129. When the cutter 306 firstmakes contact with the metal of the work being cleaned, another circuitis completed which may be traced as follows: Commencing at the positiveterminal 336 of rectifier 297, current flows through conductor 317, theterminal 312 of connector 310, the work being cleaned, the cutter 306,conductor 305, coil 301 of relay 300 and conductor 304 to the negativeterminal 337 of rectifier 297. This coil 301 of relay 300 nowdeenergizes the coil 186 of the electromagnetic means 180 and spring 171acting on pin 164 raises the spindle I and disengages the cutter fromthe work with a delay caused by the time-delay circuit 340. Upon thecutter leaving the work, the circuit through the coil 301 is broken andthe contacts 302 and 303 are closed, resetting the device for the nextoperation.

The advantages of the invention are manifest. The spindle can be soquickly raised that the cutter will only cut less than one-thousandthsof an inch of the work being cleaned. The drill press is highlyadjustable for all types of cleaning, thus preparing the surface of thework for soldering.

lclaim:

1. A depth-controlled drill press comprising:

a. supporting means b. a quill mounted in said supporting means,

c. a work rest carried by said supporting means,

d. a spindle carried by said quill and guided for rotational and axialmovement toward and from said work rest,

e. an end cutter carried by said spindle,

f. feed means for feeding the spindle and cutter toward the work rest,

g. shifting means for moving said spindle and the cutter away from thework rest independently of the feed means while the spindle is rotating,

h. control means for actuating said shifting means when the cutter hasmade contact with the metal of the work i. and power means forcontinuously rotating said spindle.

2. A depth-controlled drill press for use in removing the outer layer ofinsulation from a flat conductor mounted on an insulating boardaccording to claim 1 in which a. the shifting means including b.electromagnetic means having a normally closed electromagnet circuitholding said spindle with the cutter in operating position foradvancement by the feed means toward the work v c. a control circuitincluding normally open trigger circuit having meansadapteduponenergization to'deenergize' said electromagnet circuit, 3. Adepth-controlled drill press according to claim 1 in which:

a. the shifting means includes b. an electromagnet and t c. a magneticmember cooperating with said electromagnet to control the movement ofthe spindle independently of the feed means. 4. A depth-controlled drillpress according to claim 3 in which:

a. the electromagnet is mounted on the supporting means,

and b. the magnetic member is mounted on the spindle. S. Adepth-controlled drill press according to claim 4 in which:

a. the electromagnet has an inverted conical socket and, b. the magneticmember is conical and is adapted to be attracted by the core of theelectromagnet. 6. A depth-controlled drill press according to claim 4 inwhich: I a. the supporting means has a head and b. a body with c. guidemeans for guiding said head for movement toward I and from the workrest. 7. A depth-controlled drill press according to claim 6 in which:

a. the electromagnet has a core which is mounted on the head and has anupwardly facing conical socket and b. the magnetic member is mounted onthe spindle above the core of the electromagnet and has an invertedconical surface engageable withthe socket in the cone.

8. A depth-controlled drill press according to claim 7 in which: i

a. a spring is mounted between the body of the housing and the spindleand moves the spindle and cutte'r away from the work rest when theelectromagnet is deenergized.

9. A depth-controlleddrill press accordinglyto claim 8 in which:

a. a normally closed electromagnetic circuit actuates the electromagnetand i b. a normally open inversion circuit having the metal of the workand cutter in circuit and upon energization by the cutter engaging saidmetal, deenergizing the electromagnetic circuit.

10. A depth-controlled drill press according to claim 9 in which:

a. a relay is employed actuated by the inversion circuit and b.deenergizing the electromagnetic circuit.

11. A depth-controlled drill press according to claim 10 in which: p i

a. a two-terminal connector is employed adapted to be connected inseries with the controlled terminals of the relay and b. energized bythe same source of electricity as the inversion circuit is energized by,p

c. a pilot lamp is connected across the input to the relay and d.another pilot lamp is connected across the coil of said electromagnet12. A depth-controlled drill which: a

a. time-controlled delay means delays the opening of the electromagneticcircuit.

press according to claim 9 in

1. A depth-controlled drill press comprising: a. supporting means b. a quill mounted in said supporting means, c. a work rest carried by said supporting means, d. a spindle carried by said quill and guided for rotational and axial movement toward and from said work rest, e. an end cutter carried by said spindle, f. feed means for feeding the spindle and cutter toward the work rest, g. shifting means for moving said spindle and the cutter away from the work rest independently of the feed means while the spindle is rotating, h. control means for actuating said shifting means when the cutter has made contact with the metal of the work i. and power means for continuously rotating said spindle.
 2. A depth-controlled drill press for use in removing the outer layer of insulation from a flat conductor mounted on an insulating board according to claim 1 in which a. the shifting means including b. electromagnetic means having a normally closed electromagnet circuit holding said spindle with the cutter in operating position for advancement by the feed means toward the work c. a control circuit including normally open trigger circuit having means adapted upon energization to deenergize said electromagnet circuit,
 3. A depth-controlled drill press according to claim 1 in which: a. the shifting means includes b. an electromagnet and c. a magnetic member cooperating with said electromagnet to control the movement of the spindle independently of the feed means.
 4. A depth-controlled drill press according to claim 3 in which: a. the electromagnet is mounted on the supporting means, and b. the magnetic member is mounted on the spindle.
 5. A depth-controlled drill press according to claim 4 in which: a. the electromagnet has an inverted conical socket and, b. the magnetic member is conical and is adapted to be attracted by the core of the electromagnet.
 6. A depth-controlled drill press according to claim 4 in which: a. the supporting means has a head and b. a body with c. guide means for guiding said head for movement toward and from the work rest.
 7. A depth-controlled drill press according to claim 6 in which: a. the electromagnet has a core which is mounted on the head and has an upwardly facing conical socket and b. the magnetic member is mounted on the spindle above the core of the electromagnet and has an inverted conical surface engageable with the socket in the cone.
 8. A depth-controlled drill press according to claim 7 in which: a. a spring is mounted between the body of the housing and the spindle and moves the spindle and cutter away from the work rest when the electromagnet is deenergized.
 9. A depth-controlled drill press accordingly to claim 8 in which: a. a normally closed electromagnetic circuit actuates the electromagnet and b. a normally open inversion circuit having the metal of the work and cutter in circuit and upon energization by the cutter engaging said metal, deenergizing the electromagnetic circuit.
 10. A depth-controlled drill press according to claim 9 in which: a. a relay is employed actuated by the inversion circuit and b. deenergizing the electromagnetic circuit.
 11. A depth-controlled drill press according to claim 10 in which: a. a two-terminal connector is employed adapted to be connected in series with the controlled terminals of the relay and b. energized by the same source of electricity as the inversion circuit is energized by, c. a pilot lamp is connected across the input to the relay and d. another pilot lamp is connected across the coil of said electromagnet
 12. A depth-controlled drill press according to claim 9 in which: a. time-controlled delay means delays the opening of the electromagnetic circuiT. 